FIELD OF THE INVENTION
The invention relates to a device for recording a change in position at a turbine configuration having a turbine shaft and/or turbine blades fastened to the turbine shaft and surrounded by a turbine casing.
When a turbine, for example a steam turbine, is in operation, operational stress on a rotor having the turbine shaft and the turbine blades (moving blades), may cause changes in radial clearances or bridging of radial gaps, predominantly in a region where the rotor experiences the greatest sag. Such gap changes, which occur particularly at high temperatures, are therefore normally monitored.
In order to monitor gaps between turbine parts, it is known from International Publication Number WO 93/17296, corresponding to U.S. Pat. No. 5,572,039, to detect gap changes, on the basis of changes in light intensity, through the use of an optical waveguide led through the turbine casing and through the use of prisms disposed in the turbine casing and/or in a turbine blade. However, a disadvantage thereof is that thermal influences and the moisture of the working medium, for example steam, present in the gap, result in fogging of the prisms and the formation of scale on turbine parts. Such scaling or coatings on the turbine parts causes the intensity of the reflected light to change, irrespective of gap changes. Accurate and constant measurement of the radial gap is therefore not ensured. Furthermore, gap monitoring has heretofore not been provided in an edge region of the rotor.